The general goal of this project is to understand the molecular mechanisms and selective forces that determine the arrangement of genes in bacterial chromosomes. work includes characterization Of chromosomal rearrangements, their genetic behavior and consequences for bacterial growth. We are also studying the mechanisms that contribute to chromosome rearrangements including both legitimate recombination events and transposon mediated events. We hope to understand what selective or mechanistic factors prevent the recovery of inversion mutations for some (but not all) segments of the bacterial chromosome. We will continue to pursue evidence that chromosomal duplications are a valuable means by which bacteria adapt to environmental stress. This will include work to elucidate why particular duplications convey a greatly enhanced ability of cells to grow on limiting carbon sources. We will continue to characterize two repeated sequences found in Salmonella. One is the Salmonella-specific insertion sequence, IS200; we hope to learn why this element is limited to Salmonella and is not found in the related enteric bacteria which exchange plasmids and phages with Salmonella. The second element is the tiny REP sequence which is shared by both Salmonella and E. coli. Distribution of REP suggests that it is a degenerate tranposable element that may have acquired selective value to bacteria. We are most interested in the possibility that this element serves to mediate selectively valuable chromosomal rearrangements. Finally, we will initiate work on the mechanism of transductional recombination and the contribution of phage and host to this process. This work will be done in conjunction with other work on the recombination mechanisms and pathways involved in chromosomal rearrangement.